The present invention is directed to bicycles and, more particularly, to a power control circuit for an electromotive unit used with the bicycle.
Bicycles may be equipped with dynamos for energizing headlights and other devices. Such conventional devices are disclosed in JP (Kokai) 5-238447 and 2000-62523. In the first disclosed device, physical exertion on the rider is reduced and headlight luminance is enhanced by sensing the terminal voltage of the battery and controlling the field current of the dynamo in accordance with the sensed voltage. In the second disclosed device, a charging capacitor is provided and electric power is fed from the charging capacitor to the headlight when the dynamo generates too little electric power.
The dynamo-powered equipment of current bicycles includes not only headlights but also actuators for shifting electrically powered shifters, actuators for adjusting the damping force of an electrically powered suspension, indicator backlights for cycle computers, and the like. Such equipment will be referred to herein as xe2x80x9celectromotive units.xe2x80x9d Electromotive units begin operating unstably when the drive voltage drops below a specific level. In the particular example of a motor being used as an actuator, a reduction in the drive voltage reduces the rotational speed of the motor and makes the motor incapable of operating at normal speed. Thus, the reduced drive voltage may cause an electrically powered shifter to stop during shifting, may render the actuator of an electrically powered suspension incapable of moving in the middle of operation, and may cause other problems. A reduced voltage may cause a microcomputer used for an electromotive unit to malfunction, and a reduced voltage may cause insufficient backlighting for a display screen of a cycle computer. With such conventional devices, it was impossible to address the aforementioned problems because actuators or the like were not considered to be loads (driven equipment).
The present invention is directed to a power control circuit for a bicycle electromotive unit that helps to avoid malfunction of the electromotive unit and/or helps to avoid overcharging of a power storage device. In one embodiment of the present invention, not to be limited thereto, a power control circuit having an input for receiving power from a power source and an output for driving a bicycle electromotive unit comprises a storage unit; a first switching element disposed between the storage unit and the output; a voltage sensor that senses a voltage associated with the storage unit; and a switch control circuit operatively coupled to the voltage sensor and to the first switching element to disable the communication of power to the output when the voltage associated with the storage unit is less than a first reference voltage and to enable the communication of power to the output when the voltage associated with the storage unit is greater than the first reference voltage. If desired, after the switch control circuit enables the communication of power to the output, the switch control circuit may maintain the communication of power to the output when the voltage associated with the storage unit falls below the first reference voltage and is above a second reference voltage. Such a structure may provide a hysteresis effect to stabilize the switching operation if the switch control circuit enables the first switching element when the voltage associated with the storage unit falls below the second reference voltage.
In another aspect of the present invention, not to be limited thereto, a second switching element is disposed between the input and the storage unit, wherein the switch control circuit is operatively coupled to the second switching element to enable the communication of power to the storage unit when the voltage associated with the storage unit is less than the first reference voltage and to disable the communication of power to the storage unit when the voltage associated with the storage unit is greater than a third reference voltage. This helps to avoid the storage unit from being overcharged or otherwise contribute to the malfunction of the electromotive unit from excessive voltage.